The present invention is in the field of vehicle instruments and gauges, and more particularly to the mechanisms for driving gauge indicators such as pointers.
Pointer-type gauges are common on vehicle instrument panels. They are used for both relatively instantaneous indications of vehicle operating conditions such as speed and RPM, and for relatively slow-acting indications such as oil and coolant temperature, fuel level, battery voltage, etc. It is standard practice to drive both fast-acting and slow-acting gauges with stepper motor mechanisms, such as the one illustrated in U.S. Pat. No. 5,845,598. Stepper motors are, however, overkill for slow-acting gauges. Not only do they take up a significant amount of space in increasingly crowded instrument panels, but stepper motors and their driving mechanisms are relatively expensive.
Stepper motor drive mechanisms also require relatively large microprocessors to control them. The microprocessor must manage multiple counters (one for every input) and digital drivers (one for every output) with the result that significant microprocessor capacity is assigned to managing stepper motor arrangements.
The present invention is a gauge indicator drive mechanism especially useful for gauges on vehicle instrument panels. The drive mechanism is both simple and inexpensive. It is useful primarily for slow-acting gauges such as oil and coolant temperature, fuel level, battery voltage, and the like. The drive mechanism takes up very little space and uses minimal microprocessor capacity to run it in accordance with vehicle operating conditions affecting the gauge readout.
In its preferred form, the inventive drive mechanism is a rack and gear mechanism driven by muscle wire acting against spring tension. Muscle or shape memory actuator wires are typically made from a shape memory or bio-metallic material such as nickel-titanium alloy, and are called xe2x80x9cmuscle wirexe2x80x9d because they flex or shorten like muscles when electrical current is applied to them. The wire contracts quickly and silently, and when power is shut off, the wire relaxes and cools, returning to its original length. A typical muscle wire on the market is sold under the name xe2x80x9cFlexinolxe2x80x9d, and comes in varying specifications for voltage, current, resistance, power, mass, wire length in relaxed and contracted conditions, and wire force.
The gauge indicator in a preferred form is a pointer driven by a gear, which in turn is driven by a rack operated by the muscle wire. The rack transforms the linear contracting motion of the muscle wire into a useful driving force for a gear, which can translate a relatively small amount of linear muscle wire contraction into a significant rotational motion of the pointer using various gearing between the rack and the pointer. The rack is under spring tension in its rest position, the spring tension being increased as muscle wire attached to the rack pulls the rack against the spring force to rotate the pointer gear. The muscle wire contracts in response to electrical current supplied in the form of a signal from a vehicle component or system whose condition the pointer indicates.
The electrical signal in a preferred form is received from a microprocessor, and optionally is amplified, the microprocessor sending current to the muscle wire in proportion to a sensed vehicle condition, causing the wire to contract according to the size of the current, and thereby driving the pointer in proportionate amount over a gauge face to give the appropriate reading.